1. Field of the Invention
The present invention relates to an optical element for reflecting and/or redirecting light rays entering into it and then exiting from it, wherein the redirection or reflection is effected by means of a total reflection.
2. Description of the Related Art
Such an optical element is described for example in DE 199 23 255 A1 and illustrated in FIG. 7. This known optical element 100 consists of a plate-like base part 101 which at its upper side is occupied by a plurality of microprisms 102, which taper from their roots forming notches 103. The form of these microprisms 102 is such that light rays which enter into them from the upper side are totally reflected at the side walls 104, which has the consequence that the light rays leave the substantially flat light exit surface 105 of the optical element 100 only in a certain angular range. Due to this restriction of the light exit angle, light passing through this optical element 100 is perceived by an observer as dazzle-free.
However, an anti-dazzle effect takes place only for such light rays as enter via the upper side into the microprisms 102. In contrast, light which initially enters into the notches 103 and some time later enters info the optical element 101 is not rendered dazzle-free through the total reflection and is therefore undesired. For this reason, with the illustrated known optical element there is provided an additional cover element in the form of a grid 106 which is applied to the upper side of the optical element 100 and has light permeable regions 107 and light absorbing or reflecting regions 108. The arrangement of the light permeable and light absorbing regions 107 and 108 thereby corresponds to the arrangement of the microprisms 102 and notches 103, so that a light entry into the notches is prevented. In this way it is ensured that solely dazzle-free light leaves optical element 100 at its light exit side 105.
The production and arrangement of such a grid 106 is possible when the spacings between the microprisms 102 are sufficiently large, that is for example in the millimeter or centimeter range. However, the tendency is towards size reduction of the microprisms themselves and therewith also the spacings between them. Through this, however, it is ever more difficult to produce and arrange an exactly fitting cover grid in particular because, through heating, tolerances can become effective to such a degree that the functioning of the cover is prevented.
A similar problem arises with the light guide element known from U.S. Pat. No. 6,092,904. This consists of a flat transparent light guide body which has on one flat side a prism-like structure which is supposed to couple light rays out of the light guide element using total reflection. In order to make the total reflection possible, on its side having the prism structure the light guide body is covered over by a so-called compensation body which has a form complementary to the structure of the prisms and, with the aid of spacers, is slightly offset to the light guide body. Through this a thin gap is formed between the light guide body and the compensation body, which makes possible the total reflection at the side surfaces of the prisms. Thereby, the spacers are either separate elements which are applied before the light guide body and the compensation body are brought together, or are already formed on the compensation body, which can for example be produced in an injection molding process, in the production of the compensation body.
Also in the case of this known light guide element, for maintaining the total reflection it is of substantial significance that the light guide body and the compensation body are matched exactly to one another. If this is not the case, the provision of the gap necessary for the total reflection can no longer be ensured and the optical properties of the light guide element deteriorate. There again arises, however, the problem that the exactly matching production of light guide body and compensation body is ever more difficult and complex the smaller are the prism structures chosen to be.
From DE 196 37 199 A1 it is further known to fill the free space located between two totally reflecting surfaces of a light redirecting element with a powdery separation material. Although this separation material prevents the two reflecting surfaces coming directly into mutual contact during the production of the light redirecting element, it is problematic for the later employment of the light redirecting element. The free space filled by the separation material must later still be covered in order to prevent that the separation material later falls out again. Further, the powdery separation material does not form a homogeneous light-impermeable body which would completely prevent light entry at the notches of the light redirecting element.